1. Field of the Invention
The present invention relates to a wireless IC device preferably for use in short-range wireless communication apparatuses etc. such as an RFID (radio frequency identification) tag.
2. Description of the Related Art
Although RFID tags for the HF band are typically card-sized, small-sized RFID tags having a smaller occupation area may be required for commodity management. For the HF-band RFID tags, RFID tags utilizing a so-called sheet lamination construction method are known (see, e.g., Japanese Laid-Open Patent Publication No. 2007-102348, International Publication No. 2011/108340 and Japanese Patent No. 4535210).
The RFID tags disclosed in Japanese Laid-Open Patent Publication No. 2007-102348 and International Publication No. 2011/108340 have a lamination type antenna coil built into a multilayer substrate, and an RFIC element is mounted on the multilayer substrate. The RFID tag disclosed in Japanese Patent No. 4535210 has a plurality of interlayer connection conductors connected in a thickness direction of a multilayer substrate to form an antenna coil, and an RFIC element is mounted on the multilayer substrate.
In the RFID tags disclosed in Japanese Laid-Open Patent Publication No. 2007-102348 and International Publication No. 2011/108340, a mounting surface for mounting the RFIC element intersects with a winding axis of the antenna coil and, therefore, electrodes for mounting an RFIC chip and the RFIC element tend to interfere with formation of a magnetic field by the antenna coil. If the RFIC element is disposed outside the opening of the coil, the interference with the magnetic field formation hardly occurs; however, an occupation area is made larger.
In the RFID tag disclosed in Japanese Patent No. 4535210, the antenna coil is formed by laminating a plurality of base material layers having via-hole type interlayer connection conductors to form connection parts in the thickness direction of the multilayer substrate. Therefore, an open fault easily occurs due to a lamination deviation of the base material layers, which makes it difficult to ensure the reliability of electric connection of the interlayer connection conductors. If the base material layers are increased in thickness to reduce the number of the interlayer connection conductors, the interlayer connection conductors are increased in diameter.